Crown boundary microphones are pretty well known. The most prominent is probably the Crown PZM. However, there is another boundary mic by Crown… the PCC. It is less omnidirectional, better protected from a 200 pound foot stomp, and in a lot of ways a little less flexible. But boy does it rock on nylon-string guitar.
A set of much more expensive mics (Neumann KM-184s) were also rolling at a distance of about 12 feet away, up in the air about 8 feet in A/B configuration at about 25 centimeters.
Some folks like a blend between the two, keeping the PCCs at about 70% of the mix and fading up the Neumanns to about 30% just to add some ambience.